1. Field of the Art
The present invention relates to a combined moisture separator and reheater and more particularly a combined moisture separator and reheater capable of separating moisture contained in cycling steam discharged out of a nuclear power steam turbine.
2. Description of the Prior Art
In a nuclear power plant in which high-pressure turbines and low-pressure turbines are connected in series, steam discharged out of a high-pressure turbine is wet steam containing a large amount of moisture which not only causes erosion of the turbine blades but also reduces the turbine efficiency. Therefore, moisture must be separated from steam and the moisture-free steam must be fed into a low-pressure turbine. To this end, in a nuclear power plant, a combined moisture separator and reheater is interposed between a high-pressure turbine and a low-pressure turbine so that not only moisture contained in the steam discharged from the high-pressure turbine is separated and, at the same time, the moisturefree steam which has been reheated to a superheated state is fed into the low-pressure turbine. The moisture separator and reheater of the type described generally comprises a pair of moisture separators and reheater disposed in a single pressure shell and is disclosed in detail, for instance, in U.S. Pat. No. 3,712,272 granted to Carnavos et al., U.S. Pat. No. 3,713,278 granted to Miller et al. and U.S. Pat. No. 3,574,303 granted to Rabas.
According to the teaching of the invention of Carnavos et al. or Miller et al., a pair of moisture separator elements are disposed in a shell in the form of the letter V or inverted V and are therefore inclined relative to the vertical so that the moisture separation efficiency is decreased, whereby their length must be increased accordingly and they thus occupy a large space. As a result, there arises a problem in that the diameter of the shell cannot be reduced, and consequently the combined moisture separator and reheater cannot be made compact in size. In general, the combined moisture separator and reheater is installed on a floor upon which a steam turbine is mounted so that the diameter of the shell determines the height of the ceiling of the plant in which the steam turbines are housed. Accordingly, when the diameter of the shell is reduced, the construction cost of the turbine plant can be also reduced. U.S. Pat. No. 3,574,303 discloses a pair of moisture separating structures disposed vertically and spaced apart from each other, but a pair of tubular manifolds are received in suitable openings in the end portion and extend longitudinally into the outer chambers respectively, whereby they become obstructive to reduction in diameter of the shell. In addition, since the tubular outlet fitting for discharging drain is opening into the central chamber defined between the pair of moisture separating structures so that there arises a problem in that steam which has flowed through the moisture separating structures into the central chamber absorbs and entrains part of the drain due to the ejector effect, and consequently it becomes difficult to completely separate moisture from the cycling steam.
Furthermore, in the combined structure separator and reheater of the type described above, the temperature difference between the upper and lower wall portions of the shell reaches a value as high as 70.degree. C. in the case of the rated load operation and as high as 120.degree. C. in the case of a partial load operation because of the increase in temperature of the cycling steam. As a consequence the shell is caused to deform in the form of a humpback resulting in the damages to the joints between the shell and the partition walls which define a steam chamber.